As our understanding of sequence-to-structure relationships in proteins improves, so does our ability to rationally design new proteins and protein-based materials. Unlike discrete peptide and protein objects, the design of biomaterials requires additional rules for self-assembly to allow the nano-to-micron scale regimes to be bridged (Woolfson, D. N. & Ryadnov, M. G. Curr. Opin. Chem. Biol. 10, 559-567 (2006); Ulijn, R. V. & Smith, A. M. Chem. Soc. Rev. 37, 664-675 (2008)). In these respects, synthetically accessible peptides, which can be programmed to fold into prescribed structures and to self-assemble into larger architectures, offer routes to rationally designed peptide and protein-based biomaterials. Indeed, a variety of peptide-based self-assembling fibres, tapes and hydrogels have been produced (Zhang, S. G., Holmes, T., Lockshin, C. & Rich, A. Proc. Natl. Acad. Sci. USA 90, 3334-3338 (1993); Aggeli, A. et al., Nature 386, 259-262 (1997); Pandya, M. J. et al., Biochemistry 39, 8728-8734 (2000); Hartgerink, J. D., Beniash, E. & Stupp, S. I. Science 294, 1684-1688 (2001); Schneider, J. P. et al., J. Am. Chem. Soc. 124, 15030-15037 (2002); Paramonov, S., Gauba, V. & Hartgerink, J. Macromolecules 38, 7555-7561 (2005)). Much of this effort has been directed to the assembly of β-structured systems, though α-helix-based fibrous and α-helix-containing gelling materials have been explored to some extent (Pandya et al., 2000 supra; Petka, W. A., Harden, J. L., McGrath, K. P., Wirtz, D. & Tirrell, D. A. Science 281, 389-392 (1998); Wang, C., Stewart, R. J. & Kopecek, J. Nature 397, 417-420 (1999); Potekhin, S. A. et al., Chem. Biol. 8, 1025-32 (2001); Zimenkov, Y., Conticello, V. P., Guo, L. & Thiyagarajan, P. Tetrahedron 60, 7237-7246 (2004); Dong, H., Paramonov, S. E. & Hartgerink, J. D. J. Am. Chem. Soc. 130, 13691-13695 (2008); Gribbon, C. et al., Biochemistry 47, 10365-10371 (2008)).
In WO 2001/021646, the inventors described a self-assembling fibre (SAF) system enabling the sticky-end directed molecular assembly of α-helical coiled coils. The system comprises two short peptides (SAF-p1 and SAF-p2) of de novo design. The SAF-p1 and SAF-p2 sequences were designed to co-assemble, resulting in an offset α-helical dimer with complementary sticky ends. The ends promote longitudinal assembly into α-helical coiled-coil fibrils, which bundle to form matured fibres. Subsequently, the inventors introduced fibre-shaping peptides into the SAF system allowing morphological changes to be made to protein fibres comprising self-assembling peptides (WO 2004/022584).
In viruses (H. F. Lodish, Molecular cell biology. (W.H. Freeman, New York, ed. 6th, 2008)) and certain bacterial microcompartments (S. Tanaka et al., Science 319, 1083 (2008)), capsids and suprastructures are produced via the self-assembly of large folded proteins, usually in highly symmetric manners, and with exquisite positioning of non-covalent protein-protein interactions. Biomimetic assemblies have potential for creating simpler encapsulation systems, and for applications in controlled delivery and release, sensing, and the preparation of protocells for various aspects of synthetic biology (C. M. Agapakis, P. M. Boyle, P. A. Silver, Nat. Chem. Biol. 8, 527 (2012); D. A. Hammer, N. P. Kamat, FEBS Lett. 586, 2882 (2012); M. Uchida et al., Adv. Mater. 19, 1025 (2007)). To these ends, others have produced macroscopic “sacs” from peptide amphiphiles (R. M. Capito, H. S. Azevedo, Y. S. Velichko, A. Mata, S. I. Stupp, Science 319, 1812 (2008)); and engineered micelle-like structures (F. Boato et al., Angew. Chem. Int. Ed. Engl. 46, 9015 (2007); S. Raman, G. Machaidze, A. Lustig, U. Aebi, P. Burkhard, Nanomedicine 2, 95 (2006)), small polyhedra (N. P. King et al., Science 336, 1171 (2012); Y. T. Lai, D. Cascio, T. 0. Yeates, Science 336, 1129 (2012)), extended protein arrays (J. C. Sinclair, K. M. Davies, C. Venien-Bryan, M. E. M. Noble, Nat. Nanotechnol. 6, 558 (2011)), and metal-directed assemblies (J. D. Brodin et al., Nat. Chem. 4, 375 (2012); M. M. Pires, J. Lee, D. Ernenwein, J. Chmielewski, Langmuir 28, 1993 (2012)) using mainly natural peptides and proteins.
The inventors have produced self-assembled cage-like particles, SAGEs, from a set of short, de novo, α-helical, coiled-coil peptides by employing clear sequence-to-structure relationships and rational-design principles to direct stable and highly specific protein-protein interactions. Such sequence-to-structure relationships and rational-design principles are described in E. H. C. Bromley, K. Channon, E. Moutevelis, D. N. Woolfson, ACS Chem. Biol. 3, 38 (2008); A. N. Lupas, M. Gruber, Adv. Prot. Chem. 70, 37 (2005); and D. N. Woolfson, Adv. Prot. Chem. 70, 79 (2005).